1. Field of the Invention
The present invention relates to a method for performing with a storage control device generation management of backup data that is produced in a plurality of pairs originating from one volume, as well as to a storage control device.
2. Description of Related Art
There are storage systems that are provided with a function for generating duplicate volumes that can be used independently without the intervention of host computer software. Storage control devices used in such storage systems create a secondary volume by copying, for example, a certain logical volume (primary volume) within the storage control device in response to an external instruction, thereby forming a pair of a primary and a secondary volume.
By stopping the synchronization between the primary and the secondary volume in the formed pair and putting the pair into a split state in which each volume can be accessed separately, the resynchronization, for example, between the primary volume and the secondary volume is stopped, and the primary and the secondary volume can be used independently. For example, it becomes possible to carry out such parallel processes as performing a batch task or making a backup with the secondary volume while continuing an online task with the primary volume. As a result, it is possible to enhance the usability of the storage system.
Technology has been proposed to make it easily possible to restore original files to the state they were in at a predetermined time prior to the current time in processing backups. For example, JP H11-134234A proposes a backup and restore method including: a backup copy generating step that generates a backup copy of a given file, and a restore step that restores the original file using the backup copy generated in the backup copy generating step, which further includes, in order to allow a restoring of the file to the state it was in at a given time in the past prior to the current time, a step of designating the execution of the restore step by designating the file to be restored and the amount of time from the current time to the time in the past, and a step of selecting a corresponding backup copy based on the file designated as the file to be restored and the designated amount of time when the execution of the restore step has been designated, and controlling the execution of the restore step.
However, even though this approach “restores original files to the state they were in at a predetermined time prior to the current time,” it does not necessarily consider the synchronization of times serving as the basis for each of the processes. For example, the host computer may manage the update times of files, and the storage control device may manage the times when commands are accepted. But since there may be discrepancies between the means for keeping times in each of the devices, and since there are no attempts to synchronize the times between the devices, problems may occur when performing the restore process as explained above.
For example the following case may occur: (1) The clock of the host computer is 10 minutes ahead of the clock of the storage control device. (2) A backup is made when the clock of the host computer shows 2:00 pm. In this case, the time of the backup data will indicate 1:50 pm, which is the time that has been taken from the clock of the storage control device. (3) There is a file whose last update time is 1:55 pm, which is the time that has been taken from the clock of the host computer. (4) Thus, even though the file in (3) is actually older than the backup data, it looks newer when compared with the time of the backup data.
This means that when performing, as in the conventional related art, a restore process for “a predetermined time prior to the current time” using, for example, the time that has been obtained from the storage control device, then there is the possibility that the backup data and the files managed by the host computer are not in the correct chronological order.
Moreover, if the secondary volume is used as the backup of the primary volume, another problem occurs when a plurality of secondary volumes are generated from the same primary volume and managed, namely, the generation management of these secondary volumes is not realized. Under the condition that backup data is generated at a predetermined point in time and stored sequentially in the secondary volumes, when a restore request or the like has been received from the host computer, it was necessary to thoroughly check the content of the data in each of the secondary volumes in order to retrieve the right secondary volume when deciding the secondary volume with which the restore process should be performed. That is to say, there is a possibility that the processing takes more time, so that process efficiency deteriorates, management costs become higher, and the load on the system is increased.
The present invention is based on these considerations, and it is an object thereof to provide a method for generation management of backup data that is more efficient and has better operability.